Mercury vapor arc lamp



March 8, 1938. D. D. KNOWLES MERCURY VAPOR ARC LAMP Filed Oct. 3l,l935

INVENTORF 1). D. If/VOWZfS BY M 71/ TORNEY Patented M... s, 1938 UNITED STATES PATENT. OFFICE 2,ll0,603 MERCURY vAPoa ARC LAMP Application October 31, 1933, Serial No. 695,985

. 2. Claims. (61. 176-49) My invention relates to electric discharge devices and particularly to such devices which operate by ionization of gas or vapor, as for example, mercury vapor arc lamps.

Devices of this character find ready application I for the purposes of general illumination, particularly in the field of photography, and also in the therapeutical field due to the ultra violet light generated during operation of the tube.

Considerable'difliculty has heretofore existed in the actual operation of these devices for practical purposes due to the necessity for consider able auxiliary equipment so that they may be energized from the usual alternating current source of commercial potentials.

Moreover, the initial resistance of lamps of this type is very high requiring a breaking down of this resistance before the lamp can be started. This is usually accomplished by initiating an auxiliary discharge in order to ionize the gas or vapor within the device thus reducing the resistance thereof and causing a discharge between the main electrodes. The requisite equipment enabling the operation of such devices from the ordinary'llO volt commercial sources of electrical energy as well as rendering the device selfstarting has been not only expensive but on the whole unsatisfactory.

It is accordingly an object of my present invention to provide an electrical discharge device particularly of the mercury vapor type which may be inserted in the usual lamp socket and capable of operation from the usual domestic source of electrical energy.

Another object of my invention is the provision of an electrical discharge lamp of economical construction wherein the necessity for expensive and unsatisfactory auxiliary equipment is entirely obviated.

A further object or my present invention is the provisionof an electrical discharge device particularly of the mercury vapor type wherein the starting and maintaining of a discharge is efliciently accomplished.

Further objects of my present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein:

Figure 1 is an elevational view partly-in cross section of one form which my invention may take and in which only half waves of the alternating current are passed through the tube.

' Fig; 2 is an elevational view in cross section showing a modification of the discharge lamp shown in Fig. 1 wherein both half waves of thealternating current cycle pass through the device, and l Fig. 3 is an elevational view in cross section showing a further modification of the; discharge lamp' shown in Fig. 2 wherein both half waves of the alternating current pass. through the device and a further degree of control of the discharge may be aflected.

Referring now to the drawing in detail, I have shown in' Fig. 1 an envelope -5 of any suitable ultra-violet transparency glass, well known in the art, which may be evacuated and then filled with an inert gas, such as argon, neon, nitrogen, mercury vapor, or the like. A threaded screw base 6 of the usual type is aiiixed to this envelope at its reduced diameter or neck portion and a lead-in wire I is connected to the tip contact terminal of the base and passes through the usual stem or'press 8 of the bulb. An electrode 9 of a suitable refractory metal, such as tungsten 2 or the like, which during operation of the lamp functions as anode, is supported by the press of the envelope and is connected to the lead-in wire I by asuitable material l0 having a coeiiicient of expansion simulating that of the glass stem as is usual in the art.

The lower end of the envelope is provided with a portion of reduced diameter thus forming a cup or chamber l2 containing a quantity of nor mally liquid vaporizable conducting material, such as mercury l3, which functions as the cathode electrode of the lamp. A suitable terminal I4 is immersed in the pool of mercury and is connected to a lead-in wire I 5, extending through the wall of the envelope to the exterior thereof and provided with a material i6 similar to the material 10 at the juncture of glass envelope therewith.

This lead-in wire is in turn connected to the shell or threaded portion of the base 6 by a conductor l I in order that electrical energy may be transmitted to the cathode electrode upon the insertion of the lamp in the usual socket.

For the purpose of breaking down the initial resistance of the lamp by initiating an auxiliary discharge, I provide a starting electrode l8 of suitable material which is not deleteriously affected by the discharge of mercury vapor, such as a carborundum crystal or the like. This electrode I8 is supported by the electrode or anode 9 inelec'trical conduction therewith and projects downwardly with its depending end immersed in the mercury pool or cathode electrode i3 thus' establishing an electrical contact.

- Due to the design of my device the operating voltages thereof are such that it is preferable, whenit is inserted in the ordinary light socket, to utilize it in electrical series relationship with an incandescent lamp. Accordingly upon closure of the circuit electrical energy will be supplied through the base 6 with a positive potential impressed upon the anode 9 and a negative potential upon the cathode I3. The starting electrode I8, which is connected as before stated to the anode 9, is likewise impressed with a positive potential and, being in contact with the mercury pool or cathode l3, initiates a discharge by drawing electrons from the mercury surface and creating the formation of a cathode spot which in turn causes ionization of theinert gas within the envelope if the same is utilized.

The resistivity ofthe starting electrode material is such that the potential gradient across the meniscus of the mercury at the junction of the mercury and make-alive electrode draws electrons, as above noted, from the mercury and in this manner forms the cathode spot. The arc potential from the starting electrode to the cathode spot is then less than the resistance drop through the material to the mercury, and an arc is struck to the cathode spot from the starting electrode. When an energized anode, such as the anode 9, is present the arc will then strike from this anode to the cathode thus breaking down the initial resistance of the tube with an attendant main discharge as long as the lamp is supplied with electrical energy.

In this particular modification the discharge is a cyclic one and occurs only during alternate half waves of the alternating current cycle when the anode 9 is supplied with a positive potential from the source and the cathode I3 with a negative potential. During the remaining half waves when the potential supplied to the respective electrodes is' reversed, current will not flow due to the inherent operation of the tube as is well understood.

For the purpose of providing a lamp in which the discharge is constant during the entire alternating current cycle, I have shown a structure in Fig. 2 which differs slightly from that shown in Fig. 1 although the greater portion of the structure is identical with that previously described. In this particular embodiment of my invention I form a second cup or chamber 22 in the bottom of the'envelope 5 which inall respects is similar to the chamber I2 and this second chamber 22 likewise contains a pool of mercury 23 thus forming an electrode.

The anode 9 has its free end immersed in the mercury I3 within the chamber I2 and in like manner a further electrode 24 similar to the electrode 9 has its free end immersed in the mercury pool 23 within the chamber 22. This electrode 24 is supported by the press or stem 8 and is connected by the conductor I! to the shell of the base member 6 through a material 25 similarly to the material I0.

In lieu of supporting the make-alive electrode I3 by either of the electrodes 9 or 24 I form the same into substantially an inverted U and support it in a suitable insulated manner, such as a glass bead or the like 23, with the ends thereof inunersed in the respective mercury pools I3 and 23. When the tube shown in thismodification is energized the starting electrode I8 will again initiate a discharge. Upon energization of the device either the electrode 9 or 24 will be impressed with :agpositive potential while the remaining electrode will have a negative potential.

Assuming the anode 9 is positive at a given instant the electrode 24 will be negative thus making the mercury pools I3 and 23 positive and negative respectively. The starting electrode I8 accordingly draws electrons from the mercury surface creating the formation of a cathode spot within the chamber 22 thus breaking down the initial resistance of the lamp and causing a main discharge between this cathode 23 to the anode 9 in the same manner as previously explained.

The next half wave of the alternating current cycle the anode 9 becomes negative and the electrode 24 positive thus causing the main discharge to take place between the mercury pool I3 then acting as cathode and the electrode 24 which would be acting as anode. It can thus be seen that current would flow through the lamp during the entire alternating current cycle which would continue until the source of energy was interrupted. Moreover, due to the fact that the starting electrode I8 is immersed a substantial distance of its length in the mercury poolthere is no possibility of breaking contact, and while the mercury level on the starting electrode may change, the meniscus remains substantially constant and consequently the starting action is constant and extremely rapid, thus forming a cathode spot each half cycle of the alternating current without erratic operation of the lamp.

Referring now more particularly to Fig. 3 I have shown a modification of my discharge lamp in which a finer degree of control thereof may be effected. This modification difiers from Fig. 2 only in that I interrupt the continuity of the starting electrode I8 between the respective chambers I2 and 22.

I again support the starting electrode between the chambers by means of a stem or press 30 with leading-in wires 32 and 33 passing through the press to the exterior of the envelope and connected to a suitable switch 34. By the employment of this switch the starting circuit of the lamp may be opened or closed at will independently of any switch in the source of energy for the device.

This affords a control for very powerful lam taking perhaps as high as 50 amperes of current while the switch 34 need carry only a small starting current of a few amperes. Moreover, this circuit may be utilized for dimming or other control purposes by varying the phase or the magnitude of the current in the starting circuit.

It can thus be seen by those skilled in the art that I have provided an electrical discharge lamp particularly of the mercury vapor type which may be inserted in the usual lamp socket and energized by alternating current electrical'energy of the usual commercial potential. Moreover, the same may be readily started and efilciently maintained without the necessity of expensive auxiliary equipment.

Although I have shown and described several embodiments of my present invention, I do not desire to be limited thereto as various other modifications of the same may be made without departing from the spirit and scope of the appended claims.

What is claimed is:

1. An electric discharge device comprising an envelope provided with a screw base for insertion in the usual lamp socket and having a reentrant press, a plurality of chambers formed in said envelope and each provided with a body of normally liquid vaporizableconducting material constituting an electrode, a plurality of electrodes of each provided with a body of normally liquid -vaporizable conducting material constituting an refractory metal supported by said press and extending longitudinally of said envelope, with one end of each of said electrodes immersed in the liquid electrode material contained in each respective chamber, and a starting electrode supported by said envelope with its respective ends immersed a substantial distance of its length in the liquid electrode material contained in each of said chambers for initiating the formation of 7 an are at the junction of said starting electrode with the surface of said liquid electrode to, alternately cause a resulting discharge between one of said liquid electrodes and one of said retractory electrodes during alternate half waves 0! the alternating current cycle and to prevent deteri-' orationof said starting electrode and disengagement thereof from said liquid electrode during operation oi. said device.

-2. An electric discharge device adapted'to be energized from an alternating current source of commercial potential comprising an envelope provided with a screw base for insertion in the usual v lamp socket and having a reentrant press, a plurality of chambers formed in said envelope and electrode, a plurality of refractory metal electrodes depending from said press with the free end of each immersed a substantial distanoe in the liquid electrode contained in the respective chambers, leading-in wires passing through the press of said envelope and connecting said refractory metal electrodes to said screw base, and a starting electrode having its ends immersed a substantial distance of its length in the liquid within each respective chamber to alternately initiate the formation of an are at the junction of said starting electrode with the surface of one or the other of said liquid electrodes to cause a resulting discharge between the latter-and one or the other of said refractory metal electrodes during each half wave of the alternating current cycle and to prevent deterioration of said starting electrode and disengagement thereof from either of said liquid electrodes during operation of said device.

DEWEY D. KNOWLES; 

